In order to improve the efficiency of the combustion of fuel and air within a combustor, gas turbines typically include a diffuser designed to reduce the velocity and increase the static pressure of the pressurized airflow exiting the compressor section of the gas turbine. A diffuser may generally comprise at least one diverging diffuser wall, which allows the pressurized airflow to spread or diffuse over the length of the diffuser. However, as the pressurized airflow flows through the diffuser, friction along the diffuser wall(s) creates a boundary layer, wherein the velocity of the airflow is significantly lower than the velocity of the main airflow. Thus, the formation of a boundary layer may result in an airflow entering the combustor section of a gas turbine that exhibits a non-uniform velocity profile. This can negatively impact combustion within the combustors and reduce the overall efficiency of a gas turbine. Moreover, significant flow losses may result when the boundary layer separates from the diffuser wall, which can occur when the angle of divergence of the diffuser wall(s) is too wide. Accordingly, diffusers must typically be relatively long to obtain the necessary static pressure recovery without causing boundary layer separation.
To overcome these issues, bled diffusers are known that bleed air flowing adjacent to the diffuser wall(s) from the main airflow. In particular, a bled diffuser may be used to reduce the boundary layer size by bleeding all or a portion of the boundary layer away from the main airflow. This can reduce the likelihood of flow losses due to boundary layer separation and also produces a shorter diffuser that can accommodate wide angles of divergence to allow a significant increase in the static pressure recovery downstream from the compressor section. Consequently, however, the improved performance of a bled diffuser is often offset by the reduction in overall efficiency and performance of the gas turbine caused by bleeding pressurized air from the main airflow. Specifically, bleeding potions of the air exiting the compressor section reduces the amount of compressed air available to cool turbine components or to increase the turbine inlet pressure.
Accordingly, a system within a gas turbine that offers the benefits of a bled diffuser without the loss of efficiency and performance caused by bleeding pressurized air from the main airflow would be welcome in the technology.